I wouldn't expect Hugs to give me two different types for the same function depending on what I'd typed in at the command line. Dominic. __ __ __ __ ____ ___ _________________________________________ || || || || || || ||__ Hugs 98: Based on the Haskell 98 standard ||___|| ||__|| ||__|| __|| Copyright (c) 1994-1999 ||---|| ___|| World Wide Web: http://haskell.org/hugs || || Report bugs to: hugs-bugs@haskell.org || || Version: February 2000 _________________________________________ Hugs mode: Restart with command line option +98 for Haskell 98 mode Reading file "C:\HUGS98\lib\Prelude.hs": Reading file "C:\My Documents\functional\x690e\BEStc2.hs": Hugs session for: C:\HUGS98\lib\Prelude.hs C:\My Documents\functional\x690e\BEStc2.hs Type :? for help Main> :t unBESNULL unBESNULL :: BESable ([Char] -> Int) => BES -> NULL Main> :t (Primitive' 5 NULL) Primitive' 5 NULL :: BES Main> :t unBESNULL unBESNULL :: BES -> NULL Main> unBESNULL (Primitive' 5 NULL) ERROR: Unresolved overloading *** Type : BESable (Int -> NULL -> BES) => NULL *** Expression : unBESNULL (Primitive' 5 NULL) Main> :t unBESNULL unBESNULL :: BESable (Int -> NULL -> BES) => BES -> NULL Main> :t (Primitive' 5 NULL) Primitive' 5 NULL :: BES Main> :t unBESNULL unBESNULL :: BES -> NULL ============================== data NULL = NULL data BES = forall a . (UnBESable a) => Primitive' Int a | Constructed' Int [BES] class BESable a where bes :: a -> BES unbes :: UnBESable b => a -> b class UnBESable b where doNULL :: NULL -> b doInt :: Int -> b instance BESable NULL where bes = Primitive' 5 unbes = doNULL instance UnBESable NULL where doNULL NULL = NULL doInt x = error "Can't cast" instance BESable Int where bes = Primitive' 2 unbes = doInt instance UnBESable Int where doNULL x = error "Can't cast" doInt x = x unBESNULL (Primitive' 5 x) = (unbes x)::NULL unBESInt (Primitive' 2 x) = (unbes x)::Int ------------------------------------------------------------------------------------------------- 21st century air travel http://www.britishairways.com